dt-bindings:iio:dac:ti,dac7612 yaml conversion

Simple conversion from txt to yaml.  No significant adjustments.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
Link: https://lore.kernel.org/r/20201031134110.724233-16-jic23@kernel.org